Problems Gaining Weight...

Hi this is for a friend...

He is having alot of self esteem issues, etc. He cant gain any weight. He's 6'1 and only 130 and 25 years old. However he only eats bad foods, yeah I know. However even so, he has a tough time gaining any weight at all. What are some tips? Tests that can be done? Etc to find out what may be the cause of this, what can help? Even if he worked out, he would have a hard time gaining weight, whats a good path to follow? tests to take to make sure everythings ok. Any advice? Fasting is not an option here... Sorry. Thanks. Whats the word?

Okay - working out. Duh. But again when someone is naturally a certain way, its alot harder...??

This is causing severe self esteem problems... Thanks!